Jump to content
Sign in to follow this  

Adding Exhaust Valve to 2T

Recommended Posts

I have a 1983 IT 465 and I was wondering if anyone here has heard of a machinist machining a cylinder and adding a diaphragm controlled exhaust valve?? Would it be worth my time to head over to a machinist I know and have them customize my cylinder to accommodate a exhaust valve? I know that the newer two strokes that have them benifit greatly but can a clinder be redesigned to accomadate a exhaust valve?? I was thinking something similar to a polaris edge and escape liberty 800 motor. The valves help but they are super simple...

Share this post


Link to post
Share on other sites

I haven't seen it done without casting or cnc machining an entirely new cylinder. It is extremely common to do so on Banshee, ATC250R/TRX250R and Jet ski motors with aftermarket cylinders. They usually use a Ski-doo RAVE style valve.

It might be possible to retrofit, but it's going to end up being more effort than just buying a modern liquid cooled more powerful bike.

370gsm.JPG

350_pv_web_01.jpg

banshee_cylinder_wacces.jpg

Share this post


Link to post
Share on other sites
I It is extremely common to do so on Banshee, ATC250R/TRX250R and Jet ski motors with aftermarket cylinders. They usually use a Ski-doo RAVE style valve.

how is it controlled?

Share this post


Link to post
Share on other sites

Exhaust pressure. No control mechanism at all. Totally self contained. That's why it is "easy" to retrofit. Imagine trying to do something like a Kawasaki KIPS! Just way too many other things to add.

Pneumatically-operated power-valves are OK for rough and ragged riding, as in the snowmobile/ATV/jet-ski applications they are most commonly used. At wide open throttle, exhaust pressure lifts the blade-type power-valves, effectively raising the exhaust port for high-rpm action.

But the problem with this type of power-valve actuation for motorcycle use is that as soon as exhaust pressure drops - for instance, when rolling off the throttle when approaching a corner - so does the power-valve. So, when the throttle is rolled on again to power off the turn, the power-valve is in its lower position, and there is a 'lag', similar to turbo lag, until exhaust pressure has built up and raised the gate once again. This is more than a mere inconvenience for the motorcyclist, because the rapidly-rising power-valve will unleash masses of abrupt horsepower when it is least expected, and highsides may well result.

Any of the motorcycle powervalves are RPM-dependant, like KIPS or YPVS so they are far more predictable. The RAVE powervalves make an even less predictable power band than a non power valve engine, which doesn't matter on a CVT or jet pump... or even a sand drag banshee... but really isnt ideal for a bike, although I do know people running Cheetah cylinders on hot rodded RZ350's. It makes for a fun hooligan bike, but would unfortunately high side you on a road racing course if you actually tried to push it.

Share this post


Link to post
Share on other sites

I'm reading this cause I think it's really interesting, I have no interest in actually doing this.

But I gotta ask, wouldn't it make sense to tie this in with engine vacuum (actually lack of vacuum) to even out the rapid throttle opening causing zero to massive advance?

If you plumbed it right, you could even activate it with stored vacuum and the trigger would be exhaust pressure and lack of vacuum OR vacuum and lack of exhaust pressure.

Share this post


Link to post
Share on other sites
Exhaust pressure...

ah okay, if i remember right there were some honda's in the past with that system...

Share this post


Link to post
Share on other sites
I haven't seen it done without casting or cnc machining an entirely new cylinder. It is extremely common to do so on Banshee, ATC250R/TRX250R and Jet ski motors with aftermarket cylinders. They usually use a Ski-doo RAVE style valve.

It might be possible to retrofit, but it's going to end up being more effort than just buying a modern liquid cooled more powerful bike.

370gsm.JPG

350_pv_web_01.jpg

banshee_cylinder_wacces.jpg

Do you have info on any of those company's that perform modifications like that??

And I have a modern liquid cooled bike. I'm putting this engine into a YZ450 frame and I'm wanting to upgrade as I do it.

Share this post


Link to post
Share on other sites

'83 465 ? pretty sure they were only made '80/'81 and i dont recall a IT version but hell i could be wrong. maybe you got 490 ? anyways, should be able to put in 2 sub exh ports. need to be able to weld and know how to do porting . definatly a job for a highly experienced gear head

Share this post


Link to post
Share on other sites

1st IMO With 465cc you have enough displacement to work with to build a good powerband without an exhaust valve. Many bikes pulled it off for many years.

The RAVE is somewhat tunable with spring tension and spring preload. We would dyno a motor with the rave wide open, and again with it rigged closed. Where hp lines crossed we'd spring the raves to pop open. This gave the widest power curve. The transition onto the open valve isn't as dramatic as the pipe effect, not even close. Don't think you'd notice it much riding. Personally I think it's better system than the overly complex mechanical systems on motorcycles.

Share this post


Link to post
Share on other sites
'83 465 ? pretty sure they were only made '80/'81 and i dont recall a IT version but hell i could be wrong. maybe you got 490 ? anyways, should be able to put in 2 sub exh ports. need to be able to weld and know how to do porting . definatly a job for a highly experienced gear head

Sorry 1982. the manufacture date was like feb. 1983 but the model says 82.

Share this post


Link to post
Share on other sites

if this is going to be a project bike with a lot of different fitments to it may I suggest a later 490 jug since the exhaust port will be straight instead of angled to the side. If you wanted to add a powervalve you could study how KTM's powervalve assembly is bolted on to the front of the cylinder. machining a flat face on the front of the cylinder and welding lugs for bolt holes to hold a self contained powervalve system would be rather easy compared to figuring out at what point and how much it should open, and how it will open, or making a pipe for it. If you are an electronics engineer may I suggest electric servo tyed to your ignition like the wr 200.

or buy a kx 500 engine for your project

Share this post


Link to post
Share on other sites
Sorry 1982. the manufacture date was like feb. 1983 but the model says 82.

sounds like you got a it490. is it blue ? my dad had one back in the day and i rode it several times. was a big turd

Share this post


Link to post
Share on other sites
sounds like you got a it490. is it blue ? my dad had one back in the day and i rode it several times. was a big turd

Yes it's blue and yes it's a 465.

Blue 1981 465

Yamaha_IT465_1981.jpg

My bike (in the back ground)

000_0020.jpg

So I've been doing some research and I've found that the bigger bore bikes were more predictable without valve's.... According to what I found the Cr 500's were more agreeable than the KX500 was. That may cause some disagreements but the truth is that the 500 runs pretty dang good when tuned so my 465 should do just fine. I'll put in new reeds, polish the ports and clean up the edges in them, and I'll be ready to rip roar when I get a pipe to fit my frame (or make one).

Share this post


Link to post
Share on other sites

Pneumatically-operated power-valves are OK for rough and ragged riding, as in the snowmobile/ATV/jet-ski applications they are most commonly used. At wide open throttle, exhaust pressure lifts the blade-type power-valves, effectively raising the exhaust port for high-rpm action.

But the problem with this type of power-valve actuation for motorcycle use is that as soon as exhaust pressure drops - for instance, when rolling off the throttle when approaching a corner - so does the power-valve. So, when the throttle is rolled on again to power off the turn, the power-valve is in its lower position, and there is a 'lag', similar to turbo lag, until exhaust pressure has built up and raised the gate once again. This is more than a mere inconvenience for the motorcyclist, because the rapidly-rising power-valve will unleash masses of abrupt horsepower when it is least expected, and highsides may well result.

progressive or two stage return spring? Like fork springs. Light initially, then progressively stiffer. Should make it open easier.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×